The goal of the proposed research is to continue the rapid screening of infant cognitive measures, obtained at 9 months of age and earlier, as predictors of adult IQ. Infant twins will be assessed to establish the genetic and environmental bases of the infant measures, and their parents' IQ will be measured using the WAIS-R and a specific cognitive abilities test battery. Mean parental IQ will be taken as the best available predictor of infants' later IQ, with the strength of the relationship being estimated by midtwin/midparent correlations and regressions. In addition, however, all infant twins will now become subjects in the independently funded MacArthur Longitudinal Twin Study, providing a direct longitudinal perspective up to 3 years of age that will enhance the value of and strengthen the proposed research. During the continuation period, we will select and strengthen those infant measures showing most promise as predictors of parental IQ. These involve non-motoric, attentional, and information processing tasks. Specifically, they are Fagan's infant intelligence test based on visual novelty preference and Haith's visual reaction time anticipation task. In view of the success of the novelty and anticipation measures, an auditory novelty preference task and a manipulatory anticipation (reaching) measure will be added. Haith's visual anticipation task and the two additional tasks will be administered by him in his laboratory. Measures of complexity of vocalization and other less directly related measures such as tester ratings (IBR), hand preference, orientation tasks, and selected Bayley items also will be included. We will extend the age of testing to include 5 months so that the study will be even more relevant to early prediction of IQ, and will double the sample size to include 400 twin pairs and 100 singletons in order to put our exciting preliminary findings on a firm empirical basis. The practical significance of this research lies in the diagnostic and therapeutic benefit that will ensue from the ability to predict adult intelligence from a brief and reliable battery of measures obtained in infancy. Its theoretical significance lies in the re- evaluation of the nature of infant intelligence.